Amazon has released a Developer Preview of Fire OS 5 to those who want to test their apps on the next version of the platform. You will require an Amazon Fire HD 6 or an Android Fire HD 7 in order to install and try out the Developer Preview.
As you may know, Amazon's Fire OS which powers the company's tablets and Fire Phone is based on Android, but it doesn't come in the form you see on most devices. The current version is based on Android 4.4, though you wouldnt likely notice this due to the sheer amount of changes Amazon makes to the Android platform.
Now Fire OS 5 will be based on Android 5.0 Lollipop, which should bring all the security and performance improvements from the latest version of Android along with several new features from Amazon.
Amazon has also upgraded the App Testing Service on its Developer Portal homepage to tell developers if their apps are compatible with Fire OS 5 without having to go through the effort of acquiring and flashing a new build to their device.
If you prefer testing your apps with Fire OS 5 on physical hardware, Amazon is offering $50 off up to two Fire HD 7 tablets to developer account holders. Those interested can follow the source link to get started.
source - Amazon